Biopesticidal Effect of Partitioned Extracts of Zanthoxylum zanthoxyloides (Lam.) Zepernick & Timler on Callosobruchus maculatus (Fab.)

Abstract

Botanicals have become the focus for discovery of novel bioinsecticides for protection of crops most especially because of their biodegradability, non-toxicity, target organism specificity and environmental friendliness. Partitioned extracts of Zanthoxylum zanthoxyloides were investigated for biopesticidal effect on Callosobruchus maculatus with aim of identifying the most active components and increase ease of handling when compared to bulk crude plant material used by farmers. Crude powder of rootbark of Z. zanthoxyloides was made as well as partitioned extracts using Kupchan partition extraction methods with methanol, acetone, ethyl acetate and n-hexane as solvents. Analysis of the rootbark of the plant showed 19.87% ash content, 24% crude protein, 24.85% crude fibre, 3.13% oil extract, 15.42mg/100g alkaloids, 45.90mg/100g tannins, 1039.14mg/100g saponins, 26.47mg/100g flavonoids, 150.0mg/100g iron, 244.70mg/100g calcium, 36.65mg/100g magnesium, 449.00mg/100g potassium and 128.30mg/100g of phosphorus. The crude powder and extracts were bioassayed on C. maculatus in stored cowpea. Insecticidal activities of the partitioned extracts increased with increasing concentration; toxicity test revealed that n-hexane at 1%, 2% and 3%, acetone extract at 3%, and crude powder at 1.5g all have same effect on the insect as the positive control, achieving 100% mortality at 24 hours post treatment, number of adult emergence of 63.57 was recorded with 1% methanol extract against 28 in 3% of the extract. There was a significant difference in weight loss by the cowpea in the different fractional treatments while positive and negative controls also differed significantly (P>0.05) with all the partitioned treatments. Partition extracts from Z. zanthoxyloides were more bioactive than the crude powder, and n-hexane fractions contain the most active compounds against C. maculatus. n-hexane extract contain most active biomolecules to be explored for bioinsecticide formulation with high potency for development of new biopesticide, eliminate toxic components and increase ease of handling when compared to bulk crude plant material used by farmers.